DNA adduct formation is a common mechanism by which structurally diverse compounds can produce mutations and cancer. The enzymatic addition of 32PO4 to the 5' position of nucleotides in digests of DNA has provided a means to detect preformed lipophilic or bulky adducts on thin-layer maps. This 32p-postlabeling method was previously used in this laboratory to evaluate the profile of DNA adducts in lymphocytes of smokers and nonsmokers. We also recently used this method to measure the formation and persistence of BALB/c mouse mammary gland DNA adducts following treatment with benzo[a]pyrene (B[a]P. In the latter study, mammary glands in vivo and in vitro formed only one major adduct, 7beta, 8alpha-dihydro-9alpha 10alpha epoxy-7,8,9-10-tetrahydro B[a]P deoxyguanosine-3'-PO4. This was in contrast to liver, which formed several major adducts. The adduct profile in glands of nulliparous and parous animals was similar, as was the persistence (T 1/2 approximately 16 days) of the major adduct when measured over a four week period. The 32P-postlabeling method was also used to assess whether the formation of renal tumors in hamsters treated chronically with estrogens is associated with novel or an increased burden of DNA adducts. It was previously reported that estrogenic compounds induce indirectly novel DNA adducts that might be causally related to development of the renal tumors. The DNA of hamster kidneys treated for five months with several different natural or synthetic estrogens was evaluated for appearance of adducts. Close to a dozen intrinsic adducts were identified on TLC maps, but in repeated trials we could find no significant difference in the adduct pattern exhibited by estrogen-treated and cholesterol-treated (control) animals. On the basis of these results, we cannot confirm that new or enhanced DNA adducts as determined by 32p-postlabeling contribute to tumor formation in hamster kidneys.